You answered it in your question😉 The amount of power you can get without modifying the pcp. Daystate kinda has 3 power levels they offer. You will see the sub 12 fpe U.K. rifles then you have all their FAC rifles where you will see a max of around 60 fpe based on the caliber and then the HP series that will go as high as 70- 100 fpe depending on caliber. Those numbers are using an unmodified rifle and I have never tried to modify my HiLite .25 so I dont know how much power you can get from the non HP versions with mods.
 
Yes my answer was very specific and just the difference. I would imagine they either run larger ports and or heavier hammers and springs. If people modded Daystates like they do other rifles like the marauder we might know the answers. For all I know my Daystate wolverine can make the same power by just opening the transfer port up or installing a heavier spring. If they all have the same porting then a spring change and maybe poppet spring change and you should be able to get that same power.